1. Field of the Invention
The present invention relates to telecommunications, and more particularly, to wireless communications.
2. Description of Related Art
Emergency service calls in North America may be originated by dialing “9-1-1.” Other parts of the world may use another abbreviated string of dialable digits, such as “6-1-1” in Mexico, for example. These abbreviated strings of digits are intended to simplify an emergency call for help with an easy to remember number. These emergency calls may be routed to a local Public Service Answering Point (“PSAP”) call center to enable the initiation of an emergency response (e.g., police, fire department, road repair, and/or ambulance) while the caller is kept on the phone. If, however, the call is somehow disconnected or dropped before the emergency is completely reported or the responder arrives, the PSAP call center may be required to call back the originator.
Presently, a record for a “9-1-1” call originated through a wired network may include Automatic Line Identification (“ALI”) or the telephone number of the access line from which the call originated. The directory number (“DN”) or telephone number of a wireless subscriber may not, however, be associated with a physical line or wireless unit. Calls to a roaming wireless subscriber are routed to the wireless unit by way of the mobile station identification (“MSID”), as opposed to the mobile DN (“MDN”). Accordingly, performing an emergency call back to a wireless unit poses hurdles not encountered with landline devices, for example.
The MSID may typically be characterized as either a 10-digit mobile identification number (“MIN”) or a 15-digit International Mobile Subscriber Identifier (“IMSI”). The IMSI may be programmed into a wireless unit or a Subscriber Identity Module (“SIM”) card by the service provider with whom the wireless unit user has entered into a service agreement. Accordingly, the MSID may not necessarily be a dialable number.
The DN of a wireless unit is a dialable number. The DN is dialed by a caller and used to route a call through the network to the wireless subscriber's home system. At the subscriber's home system, the home location register (“HLR”) contains the MSID associated with the subscriber's DN. The MSID, as opposed to the DN, may then be used to route the call through the network to the serving wireless system and page the subscriber. The subscriber's DN may be provided to the serving system from the SIM card through the wireless unit or by the home system to the serving system in a separate data file called the subscriber profile.
The rollout of systems employing a separate number for DN and MSID is a relatively recent occurrence for some wireless systems. Others have used this technique since their inception. Historically, the mobile identification number of a wireless unit was the same as the DN for some systems, particularly in systems supportive of TIA/EIA-41 standards, prior to implementing wireless number portability (“WNP”) or thousands block number pooling (“TBNP”) based on the Local Routing Number (“LRN”) method and international roaming (“IR”). However, with WNP and TBNP, the MDN became “portable” or “poolable” from one service provider to another service provider. Since a MSID may not be portable or poolable, the recipient service provider may assign a new MSID for a subscriber with a ported-in or pooled MDN.
International roaming has also forced the separation of MSID and MDN. While the MIN is a 10-digit number modeled after the North American Numbering Plan's 10-digit MDN, other nation's carriers using a different directory numbering plan may not allow their subscriber's DN to be equivalent to the internationally recognized MIN format. Another standard MSID is the IMSI. It may be used in TIA/EIA-41 and GSM systems around the world. IMSI is a 15-digit non-dialable number based on ITU-T Recommendation E.212, and therefore, may not serve as a 10-digit MDN.
Historically, when the MDN was the same as the MIN, the MIN would be delivered to a PSAP call center and would be used as a call back number. With the separation of MIN and MDN as described above, it became necessary to deliver the MDN as a separate call back number to the PSAP call center, as well as the caller's MSID. There are certain problems, however, associated with implementing this solution. One issue is that the serving system may not have the caller's MDN, only the MSID, to present to the PSAP call center with the call. Some of the reasons for this relate to the way MSID-MDN separation has been implemented according to standards. Another reason is that the network interface used to deliver the call to the PSAP call center may not have the capacity to signal both the DN and MSID or, in some cases, even a full DN.
An old serving TIA/EIA-41 system may not support WNP, TBNP or IR. This means that the older serving system may be expecting the MIN and the MDN to be the same. The older system would not even know to look for a separate MDN in the subscriber's service profile (e.g., keyed on MIN, not MDN). With this limitation, these subscribers may not be allowed to use basic services, but they must be allowed to call for emergency services. As a result, a roamer who dials “9-1-1” while on an old system will have his or her call delivered to the PSAP call center with an MSID but no MDN. Accordingly, no call back is possible.
A newer serving system that is WNP and IR capable may not be able to deliver MDN to the PSAP call center. This could happen if the calling wireless unit is not registered with any service provider (e.g., there are mobile phones used for emergency calls only). These wireless units may be referred to as non-subscriber initialized (“NSI”) phones. It is also possible for a subscriber to place an emergency call before the HLR has responded to the serving system with the subscriber's service profile containing the DN. Even if the PSAP call center has been provided with a working DN for callback, the callback to the DN will not go through if the subscriber has call forwarding service for all inbound calls or if the subscriber has a limited, pre-paid service and there is no remaining balance available to pay for the inbound callback from the PSAP call center. Further, if the callback number is to a visiting international roamer, the PSAP call center may need to place an international call. Some PSAP call center may not have the ability to callback an international number. There is also the risk of network congestion or delay in completing an international call that would be detrimental to handling an emergency in a timely manner. Some PSAP call centers may not even be equipped to place any outbound calls through separate, outbound administrative lines.
The call back DN for an international roamer would require the PSAP call center to place an international call to reach a subscriber in their local Emergency Service Zone (“ESZ”). This is not a practical, timely or sufficiently reliable solution for a PSAP call center that normally does not place international calls and for applications that may require immediate call back information for emergency purposes. In addition, the entire international MDN (up to 15 digits including a country code) may not be presented to the PSAP call center for call back if the PSAP call center only supports 10 digits.
It is also possible that the calling wireless unit is not registered with any service provider. As a result, there may be no DN associated with the wireless unit or no permanent MSID encoded in the wireless unit—such wireless units are referred to as NSI mobile phones, for example. This could be because (a) the NSI phone was never intended to be registered (there are such phones to use for emergency calls only), (b) the phone is new and has not yet been initialized by a service provider, (c) the subscription has expired and the NSI phone is no longer registered with a service provider or (d) the SIM card is lost, stolen, or simply never been inserted or been removed either advertently or inadvertently.
Some wireless units also support a removable User Identity Module (“R-UIM”) or SIM that may contain the MSID and the DN. If the R-UIM or SIM are not in the phone, then it can still be used to place an emergency call. However, there is no DN or MSID known to the phone or the serving system to provide the PSAP call center as a call back number.
Every MS contains a unique mobile equipment identification number (“MEIN”) or mobile terminal identifier (“MTID”) encoded in the phone by the manufacturer. The MTID may be, for example, an electronic serial number (“ESN”), as used in ANSI/TIA/EIA-41 systems or an International Mobile Equipment Identity (“IMEI”) used in GSM systems. The MTID is independent of the MSID and DN. The MTID is signaled over the air between the wireless unit and the base station of a wireless system with a call origination attempt or soon thereafter. For example, if not supplied with the call origination attempt, the MTID may be requested by the serving system.
Current standards for wireless emergency services call for delivering “9-1-1+ the last seven digits of the MTID” to the PSAP call center as the form call back number when the directory number assigned to the wireless subscriber is not available. While this may serve to notify the PSAP call center that no working callback number is available with the call, the string of “9-1-1+the last seven digits of the MTID (MTID7)” do not uniquely identify the call (i.e., many emergency calls may be identified by the same “9-1-1+MTID7) and is not a routable number through the network. The “9-1-1+ the last seven digits of the MTID” do not contain a complete MTID, and therefore is not unique.